Electrical motors for use in high power offshore submersible pump applications, such as oil wells, typically use three-phase asynchronous induction motors with two poles and a distributed winding. The low pole number enables high speed operation at around 3500 rpm when using 60 Hz supply. The induction motors are also typically driven by a variable frequency drive that enables operations at varying speeds depending on the required flow rates through a submersed pipe.
Due to the high temperature in the well improper cooling and overloading can result in breakdown of ground wall insulation leading to stator inter-turn and phase-to-ground faults. Additionally, due to the long length of the electric cable providing power to the electric motor, there is an increased risk of a reflected voltage wave increasing the instantaneous voltage at the motor terminals above their rated value, especially during start-up of the motor. This phenomenon can also lead to insulation breakdown and cause phase-to-phase or phase-to-ground faults. Such faults lead to the loss of one or more phases, rendering the motor inoperable and in need of replacement. Typical motors, have overlapping end windings allowing faults to migrate to healthy phases leading to phase-to-phase faults.
When a motor fails it may need to be replaced. Replacing an electrical motor, such as in a submersible electronic pump, may be time consuming and costly.